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Moment of inertia for this assembly

  • #1

Homework Statement


A slender rod is 80.0 cm long and has mass 0.120 kg. A small 0.0200-kg sphere is welded to one end of the rod, and a small 0.0500-kg sphere is welded to the other end. The rod, pivoting about a stationary, frictionless axis at its center, is held horizontal and released from rest. What is the linear speed of the 0.0500-kg sphere as it passes through its lowest point?

Homework Equations


Ip = Icm + Md2
Moment of inertia slender rod Ir = ML2/12
-||- solid sphere Is = 2/5 MR2

The Attempt at a Solution


I'm right around the corner to solve this, I just need to find the sum of the systems moment of inertia. I have the center of mass of the system, I also know that I have to use the parallel axis theorem but I don't have the radius of the small spheres so I don't know how I am supposed to calculate their moment of inertia.

Or should I be able to solve it without knowing the total moment of inertia?
 

Answers and Replies

  • #2
BvU
Science Advisor
Homework Helper
2019 Award
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You can consider the spheres as point masses on the basis of the term 'small' in the problem statement.
 
  • #3
Thanks! That was what I had to do!
 

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